1. Field of the Invention
The present invention relates generally to valves for processing systems. Particularly, the present invention relates to throttle valves for vacuum systems.
2. Description of the Prior Art
Various types of valves have been devised for use in vacuum processing systems. The types of valves include gate valves, butterfly valves, multi-vane valves, and the like. Some gate valves are designed for opened and closed positions to allow for either full flow or no flow of gaseous fluids through the valve. Butterfly valves are relatively simple in design but have limited ability to achieve a linear conductance response. Multi-vane valves provide more precise control than butterfly valves.
One example of a multi-vane valve is described in U.S. Pat. No. 6,293,306 (Brenes, 2001). Brenes discloses a throttle gate valve that includes an upright, generally rectangular valve housing. Within the valve housing is positioned a linearly movable gate valve for closing off a thru-opening formed in the lower part of the valve housing. A pneumatic actuator assembly provides for moving the gate valve between an opened and a closed position. A throttle valve assembly compartment forms the lower side of valve housing and frames the through opening and includes a set of throttle vanes rotatably positioned within the through opening. A drive actuator is provided for rotating the vanes and includes a drive actuator compartment and a motor for controlling the position of the throttle vanes. The drive actuator is sealed by a bellows shield at the point where the drive actuator extends into the interior of the housing.
Another type of multi-vane valve is a throttle valve sold under the trademark “Vari-Q” by MeiVac, Inc. The MeiVac throttle valve includes a circular valve chamber containing a plurality of counter-rotating, triangular (i.e. pie shaped) vanes that are interconnected by a low friction cable-drive system.
Still another type of multi-vane valve is a fixed-positioned vane valve sold under the trademark “Temescal” by Ferrotec (USA) Corporation as part number 0627-0624-0. This multi-vane valve is not truly a valve since all of the vanes are in a fixed position in the range of 30-45 degrees, which are in fluid communication with cryogenic pumps. The vanes are each brazed to a stainless steel tube that is transverse to all of the vanes. The vanes act as a heat shield as well as to transfer heat to the stainless steel tube that contains cooling water flowing through the tube. FIGS. 1A and 1B illustrates an example of such a fixed, multi-vane valve showing a front view and a cross-sectional side view of the structural relationship of the cooling tube and the plurality of fixed vanes.